Wye-delta Contactor Burn Marks [pics]

[kaon]

Hi all,

check out these pics:

 

http://img237.imageshack.us/img237/7387/ch4starter02uj6.jpg

 

http://img513.imageshack.us/img513/5575/ch4starter03bw6.jpg

 

http://img180.imageshack.us/img180/1369/ch4starter01dc4.jpg

 

As you can see, these are Telemacanique "LC1 F 265" and "LC1 F 185" contactors.

They are used in a 300-rton chiller.

For the past few months, the chiller has been intermittently causing trips in large upstream circuit breakers. We are not sure of the cause, but these contactors do look dodgy, any ideas?

 

TIA

[jraef]

In general, Y-Delta is already a "dodgy" way to start a motor. You get a transition spike every time they switch from Y to Delta, and depending on the phase angle at the moment of transition (which you have no control over), the spikes can be as high as 20x normal! So flash marks such as those are commonplace in Y-Delta starters; they signify the beginning of the end of the contactors. Most people who decide to use Y-Delta do not understand this and use it simply because it is cheap up-front. In reality, they just shift the cost burden to people who are maintaining the equipment at a later date. In this case, that appears to be YOU! by the way, when you get flash overs like that, it also means that there were corresponding torque spikes at the same time, meaning that your mechanical components are getting beaten to death as well.

 

If it were me, I'd yank the Y-Delta and replace it with a soft starter; it will cost you less in the long run.

[kaon]

In general, Y-Delta is already a "dodgy" way to start a motor. You get a transition spike every time they switch from Y to Delta, and depending on the phase angle at the moment of transition (which you have no control over), the spikes can be as high as 20x normal! ...

If it were me, I'd yank the Y-Delta and replace it with a soft starter; it will cost you less in the long run.

 

Thanks for the info!

 

Can anyone suggest a suitable model + size soft-starter + approx cost, please? (Ball park is helpful)

Nameplate of this chiller (Trane ERTHA300) says: 194 kW input power and 314 amps full load current. 3-phase 400V mains here.

 

The Telemacanique dealer has quoted the local equiv of abt 1275 USD for supply those 3 contactors.

 

And another dealer has quoted abt 13,000 USD for a suitable VSD (aka "inverter"). Do these prices sound right?! He told me that a soft-starter would cost about the same as the VSD.

How large would a suitable soft-starter be? All else being equal, I prefer if it didn't take up more space than the Y-delta.

 

Also, what about the losses of a soft-starter when running steadily at full speed?

This might be a significant concern for a chiller that runs continuously for 12 hours daily, 7/365/yr.

[marke]

Typical pricing here would give you a soft starter for about one third of the price of a VSD.

 

For this application, you could look at the Emotron MSF310, or the Motortronics VMX-360-BP

There are many other otpions.

 

If the starter is installed without a bypass contactor, the losses would be in the order of 1KW. With a bypass contactor, the losses will reduce to the contactor fuse and switch losses so may be close to the star/delta losses.

 

Best regards,

[jraef]

Thanks for the info!

 

Can anyone suggest a suitable model + size soft-starter + approx cost, please? (Ball park is helpful)

Nameplate of this chiller (Trane ERTHA300) says: 194 kW input power and 314 amps full load current. 3-phase 400V mains here.

 

The Telemacanique dealer has quoted the local equiv of abt 1275 USD for supply those 3 contactors.

 

And another dealer has quoted abt 13,000 USD for a suitable VSD (aka "inverter"). Do these prices sound right?! He told me that a soft-starter would cost about the same as the VSD.

How large would a suitable soft-starter be? All else being equal, I prefer if it didn't take up more space than the Y-delta.

 

Also, what about the losses of a soft-starter when running steadily at full speed?

This might be a significant concern for a chiller that runs continuously for 12 hours daily, 7/365/yr.

 

We don't know where you are, but that statement of a VFD being the same price as a soft starter is just plain false wherever you are!

 

Marke is right, a soft starter with a bypass will have no more losses than the Star-Delta starter.

[kaon]

We don't know where you are, but that statement of a VFD being the same price as a soft starter is just plain false wherever you are!

Marke is right, a soft starter with a bypass will have no more losses than the Star-Delta starter.

 

Typical pricing here would give you a soft starter for about one third of the price of a VSD.

For this application, you could look at the Emotron MSF310, or the Motortronics VMX-360-BP

 

Thanks marke and jraef, that's very helpful info.

I'm in South East Asia, and have found a Telemecanique softstarter (ATS48C41Q) for the equiv of US$3900.

[NAGA]

In general, Y-Delta is already a "dodgy" way to start a motor. You get a transition spike every time they switch from Y to Delta, and depending on the phase angle at the moment of transition (which you have no control over), the spikes can be as high as 20x normal! So flash marks such as those are commonplace in Y-Delta starters; they signify the beginning of the end of the contactors. Most people who decide to use Y-Delta do not understand this and use it simply because it is cheap up-front. In reality, they just shift the cost burden to people who are maintaining the equipment at a later date. In this case, that appears to be YOU! by the way, when you get flash overs like that, it also means that there were corresponding torque spikes at the same time, meaning that your mechanical components are getting beaten to death as well.

 

If it were me, I'd yank the Y-Delta and replace it with a soft starter; it will cost you less in the long run.

 

Hi Jraef,

 

What about the closed transition star delta starter? We can avoid the spikes during transition as there is no break. Why this is not so poular? Is cost of this type more?

[marke]

Hello Naga

 

Welcome to the forum.

 

The closed transition star delta (wye delta) starter is more expensive than the standard open transition starter.

To convert an open transition starter to a closed transition starter, you must connect an auxiliary delta contactor across the existing delta contactor with large resistors in series. The resistors should be sized such that when the aux delta contactor closes, and the star contactor is open, the current through the motor windings and resistors should be in the same order of magnitude as the star current. This makes these resistors significant resistors and are approaching the resistor sizing that would be used for a primary resistance starter.

If these resistors are correctly selected, there is a period (short time) where the main contactor is closed, the star contactor is closed and the auxiliary delta is closed. This results in a high current through the resistors as they are essentially star connected across the three phases. There is still a short term high current, but there is no open transition transient and associated torque transient.

 

The control sequence is :

1. Close main contactor and star contactor
2. Wait for a period of time to allow motor to accelerate in star
3. Close aux delta contactor. Current flows through motor windings to star point. Current flows through resistors to star point.
4. Open star contactor. Current flows through the motor windings, through the resistors and back to line.
5. Close delta contactor. Resistors are now shorted out.
6. Open aux Delta contactor.

So you need to add a significant contactor, same a delta contactor, plus significant resistors, plus a complex timer. Cost is high relative to a standard open transition star delta starter.

 

- In many cases, the star delta starter is used because the supply regulations call for a reduced voltage starter, not in a real attempt to gain a performance advantage.

 

Best regards

[jraef]

And to finish that thought, usually I have found that a Closed Transition Y-Delta starter will end up being roughly the same cost of the solid state soft starter.